1. Field of the Invention
This invention relates to a system for increasing heat output in a specific section of a pipeline using an internal wire impedance system.
2. DESCRIPTION OF THE PRIOR ART
Pipelines often require the fluid flowing in them to have lower viscosities than they would have at the ambient temperature of the pipe. In order to reduce the viscosity of the fluid, heat is generally transferred into the fluid. A way to achieve this is through steam tracing, that is, a system which uses steam flowing in a separate conduit adjacent to the one transporting the fluid. Another system is one using alternating current and the effects of a magnetic field produced by the current to increase the temperature of the fluid in the flow pipe. This second method has in the past been called "skin effect heating," or more correctly, "internal wire impedance heating."
Industry has used the skin effect or internal wire impedance heating which, under current practice, uses a ferromagnetic pipe attached substantially parallel and either interior or exterior to a fluid-flow pipe. The ferromagnetic pipe has longitudinally extending through it an insulated copper wire that is electrically connected to the ferromagnetic pipe at a point remote from the point of entry of the insulated wire. This allows both the wire and pipe to be connected in series with each other and a source of alternating current power. Thus, the electric current flows through the insulated wire and returns through the wall of the ferromagnetic pipe. Due to the skin effect, most of the current flows near the inside wall of the pipe.
Heat is generated in the wall of the ferromagnetic pipe by magnetic hysteresis resulting from a type of internal friction as the magnetic domains within the pipe wall are reversed; eddy currents in the pipe wall due to the presence of the pipe wall in a changing magnetic field which induces currents to circulate throughout the pipe wall yielding an I.sup.2 R heating effect; and the I.sup.2 R effect of the current returning through the pipe wall. Additional heat is also generated in the insulated wire according to Joule's Law, i.e., the I.sup.2 R effect of the current flowing in it.
A point worth mentioning here is the reason for using a pipe having the property called "ferromagnetism." It simply is that this property greatly increases the magnetic field in the pipe wall due to the alternating current through the conductor, which results in significant heating by hysteresis and eddy currents. Examples of ferromagnetic elements are iron, nickel and cobalt. Additionally, a few alloys may have components which by themselves are not ferromagnetic, but when combined as an ally exhibit this property, e.g., MnBi.
In prior installations of internal wire impedance heating systems of which I am aware, a standard way to further increase the heat output of a given section of pipe for any length of time does not exist. The present invention, however, includes several embodiments which do increase the heat output for a given section without affecting the heat output of any adjacent section. The utilization of the present invention results in both an economical and efficient use of electrical power.
An example where economy and efficiency result is when a portion of buried heated pipeline is located above ground, and the ambient temperature is very low. The portion above ground will have a greater heat loss, and will consequently require more heat. Similarly, it is desirable to have a heat increase through a section that has less effective insulation or the pipe has a section of increased diameter.
Additional uses and advantages of this invention will become evident from the summary of invention, the drawings and the description of the preferred embodiment.